U.S. Pat. No. 5,563,504 entitled “Switching Bandgap Voltage Reference” by inventors Barrie Gilbert and Shao-Feng Shu describes a switched capacitor network which is used in conjunction with a single PN junction to form a switching bandgap reference voltage circuit. Gilbert's circuit is based on bandgap references that add a diode voltage to a VPTAT (voltage proportional to absolute temperature) voltage. The diode voltage has a negative temperature coefficient while the VPTAT voltage has a positive temperature coefficient. By properly choosing the two voltages, the temperature effects cancel out which provides a combined voltage that is independent of temperature over moderate temperature ranges.
A fundamental problem with the Gilbert cell is that it requires a supply voltage greater than 1.25 Volts (V). Also, the optimal operating point occurred when the two voltages with opposite temperature coefficients summed to about 1.24V. There are a variety of ways of accomplishing a substantially similar result with other configurations. Also, configurations are known which provide voltage references at other voltage levels. Many of these configurations, however, are not suitable for providing a low voltage reference level, such as a voltage level below 1V. Also, many of these configurations consume appreciable amounts of power and are not suitable for low power applications.